Canīt install internal cable on Cube Reaction frame

Hello,

I'm a newby in the matters of bike mechanics but I recently decided to build my own mtb.

Now that I'm in the end (I think) of this painful process I'm facing a irritating problem. I can't insert the front derailleur internal cable. The hole seems obstructed because I feel something soft in the end of the cable at half way.

Can it be the rubber cable inside the frame? If yes maybe it's curled or out of position...